The present invention relates to an imaging lens for forming an image of an object on an imaging element such as a CCD sensor and a CMOS sensor, and particularly, it relates to an imaging lens suitable for mounting in a relatively small camera such as a built-in camera of a portable device including a cellular phone and portable information terminal, a digital still camera, a security camera, a vehicle onboard camera, and a network camera.
In these years, in place of cellular phones that are intended mainly for making phone calls, so-called “smartphones” have been more widely used, i.e., cellular phones with such functions as those of portable information terminals (PDA) and/or personal computers. Since the smartphones generally have more functions than those of the cellular phones, it is possible to use images taken by a camera thereof in various applications. For example, while it is possible to use the smartphones for printing and enjoying images taken, it is also possible to use images in other usage such as processing images to use for game characters or for makeup simulations, dress fitting simulations, and the others. The ways of the image usage were not conventionally common, however, it becomes more common mainly among young people
Generally speaking, product groups of cellular phones and smartphones are often composed of products of various designs for the ones for beginners to the ones for advanced users. Among them, an imaging lens to be mounted in a product, which is developed for advanced users, is required to have a high resolution lens configuration so as to be also applicable to a high pixel count imaging element of these days. However, as the imaging lens to be mounted in a smartphone used for the above-described usages, it is critical to be a small size and has a wide angle of view, that is, a wide angle, than having a high resolution.
However, it is also true that even products for beginners require a certain degree of high resolution. In case of a lens configuration composed of six lenses, since the number of lenses that compose the imaging lens is many, although it is slightly disadvantageous for downsizing of the imaging lens, the degree of freedom upon designing is high, so that there is potential for achieving both satisfactory aberration correction and downsizing of the imaging lens in a well-balanced manner. As an imaging lens having the six-lens configuration, for example, an imaging lens described in Patent Reference has been known.
The imaging lens described in Patent Reference includes a first lens that is negative and has a shape of a meniscus lens directing a convex surface thereof to an object side; a bonded lens that is composed of two lenses, positive and negative lenses; a fourth lens that is positive; and a bonded lens that is composed of two lenses, positive and negative lenses, being arranged. According to the imaging lens described in Patent Reference, satisfying a conditional expression regarding a curvature radius of an object-side surface and an image plane-side surface of the first lens and a conditional expression regarding the two bonded lenses respectively, it is achievable to satisfactorily correct a distortion and a chromatic aberration. Patent Reference: Japanese Patent Application Publication No. 2011-145315
According to the imaging lens of Patent Reference, however, since a distance from an object-side surface of the first lens to an image plane of an imaging element is long, for mounting the imaging lens in a small-sized camera such as a cellular phone and a smartphone, it is necessary to dispose a prism or a mirror between the imaging lens and the image plane so as to bend a light path. High functionality and downsizing of cellular phones and smartphones are advanced every year, and the level of downsizing required for the imaging lens is even higher than before. With the lens configuration described in Patent Reference, it is difficult to attain satisfactory aberration correction while attaining downsizing of the imaging lens so as to meet the aforementioned demands.
Here, such an issue is not a problem specific to the imaging lens to be mounted in a cellular phones and smartphones, and rather, it is a common problem even for an imaging lens to be mounted in a relatively small camera such as digital still cameras, portable information terminals, security cameras, onboard cameras, and network cameras.
An object of the present invention is to provide an imaging lens that can satisfactorily correct aberrations. A further object of the present invention is to provide an imaging lens that can attain both downsizing of the imaging lens and satisfactory aberration correction.
Further objects and advantages of the present invention will be apparent from the following description of the present invention.